As has been said a few times there are loads of hurdles to jump over to do it 'right' For sure NMS proved we can have it now, but the big things lacking (from a space sim pov) from NMS are graphics fidelity, consistency and realism.
All these things not only take a tremendous amount of compute power (both CPU and GPU) they also take an awful load of design work to look 'right'
Now probably today's Pascal Titan X and 1080's could do a lot of the gfx work but that would set the bar of entry so high it would restrict sales. So basically even if it can be implemented using todays high end tech you'd need to wait until today's high end is tomorrow's mid range(i.e going on current trends in about 2 years time)
There's also the gameplay elements. You'd want so many other systems in place to maximise the gameplay experience. For example
multi-crew
Avatar creation/customisation
Walking around/1st person
Better chat and socialisation tools
Ideally VR support
Stuff to shoot at/do when landed.
To name but a few
So yeah, not expecting it for at good 2-3 years
Restrict sales? I already bought Horizons with the impression that later worlds would be included upon completion. I will probably buy all the seasons upon release. However landing on Earth like worlds will be behind another pay wall?